In the manufacture of semiconductor devices, a large diameter silicon wafer is secured by an adhesion tape (known as dicing tape) and subjected to a dicing (sawing and separating) step where the wafer is divided into semiconductor chips. The chips are then peeled from the dicing tape. Each chip is picked up and secured to a lead frame with a curable liquid adhesive (or die bonding agent) through heat compression bonding. In the current industry, a rational process capable of carrying out dicing and die bonding steps continuously is needed, and the contamination of semiconductor parts with fluid ingredients from the liquid adhesive and the squeeze-out of the adhesive from chip securing sites are also issues of concern. It is then desired to have a dicing/die bonding tape in the form of an adhesion sheet having an adhesive layer of non-liquid adhesive and possessing both the wafer-securing function of dicing tape and the bonding function of die bonding agent. The dicing/die bonding tape needs to develop a tack force (or attachment) enough to prevent chips as diced from being moved or released during the dicing step, to adhere to the chip being taken away in the pickup step, and to develop a strong bond to the lead frame in the subsequent die bonding step.
Such a dicing/die bonding tape is disclosed in JP-A 9-67558 as a sheet comprising a plastic film substrate and a dicing/die bonding layer of thermoplastic polyimide resin. In an embodiment, a wafer is secured to the polyimide resin layer in close contact with the substrate by heat compression, and is diced in this state. Each chip is picked up with the polyimide resin layer bonded thereto and attached to a lead frame by heat compression and heat bonded thereto.
However, since the polyimide resin layer and the wafer are firmly joined by heat compression, the wafer holding and chip pickup depend on the bond between the substrate and the polyimide resin layer and are not easily controlled. Another drawback is that the adhesive layer of thermoplastic polyimide resin are insufficient in adhesion, especially adhesion in moist conditions, adhesion at elevated temperature and strength which are required in wire bonding, sealing and solder reflow steps during the manufacture of semiconductor devices.
JP-A 2002-256236 discloses a dicing/die bonding tape in which a layer of a resin composition comprising (A) a polyimide resin, (B) an epoxy resin, (C) a phenolic resin, and (D) a curing accelerator, which composition is improved in adhesion in moist conditions and adhesion at elevated temperature, is formed on a film substrate having thereon a radiation-polymerizable adhesive layer capable of controlling bonding or adhesion as reported in Japanese Patent No. 2,984,549.
This die bonding layer composed of the curable epoxy resin composition is improved in adhesion in moist conditions, adhesion at elevated temperature and strength, but sometimes hinders the chips as diced from being picked up. More particularly, the radiation-polymerizable adhesive layer which controls the adhesion between the substrate and the die bonding layer as reported in Japanese Patent No. 2,984,549 is formed of a composition comprising a (meth)acrylate copolymer, (meth)acrylic radical-containing polymer or polyfunctional acrylic compound and a photo-polymerization initiator. This composition is compatible with the die bonding layer. On account of reaction due to UV exposure or fusion between the adhesive and the die bonding layer which is softened by heat compression for wafer holding in the dicing step, the tack strength is increased to prevent the chips from being easily picked up. The tack strength (or adhesive property) between the die bonding layer and the radiation-polymerizable adhesive layer changes or increases with the passage of time, also preventing the chips from being easily picked up.